This invention relates to new nitrohumic acid-containing adsorbents possessing high mechanical strength and to a process for producing same.
The adsorbents are utilizable effectively for adsorbing heavy metals and oils contained in water.
It is known that nitrohumic acid exhibits high absorptivity for heavy metals dissolved and oils afloat in water. However, this compound is low in mechanical strength when shaped into granules and is finely pulverized under even slight pressure when charged into a packing tower. In addition, this compound has the disadvantage of partially dissolving when used for treating an alkaline or neutral solution, resulting in coloration of the solution in yellowish brown. If this compound is incorporated with a conventional binder to enhance mechanical strength, the excellent heavy metal adsorbability inherent to nitrohumic acid suffers. Therefore, nitrohumic acid has not yet had practical use as a heavy metal adsorbent for the treatment of waste effluents, notwithstanding the cheapness of this compound.
We have found that when a carboxyl group-containing polymeric compound such as carboxymethylcellulose or alginic acid is added as a binder to nitrohumic acid and the mixture is shaped into granules, an adsorbent of good quality is obtained, which is improved in mechanical strength while retaining the good adsorptivity inherent to nitrohumic acid.
As the result of many researches made on adsorptivity of such adsorbents under various conditions, however, it has now been found that adsorptivity of these adsorbents for heavy metals, especially mercury is seriously disturbed when a significant amount of chlorine ion is present. Thus, a certain type of improvement will be necessary for such adsorbents when they are used for the treatment of aqueous effluents containing heavy metal ions together with chlorine ion.